1. Field of the Invention
The present invention relates to a novel process for preparing basic aluminum compounds having a high yield of a polymeric species with increased reduced sweat activity. More particularly, the present process prepares a single species of the basic aluminum compounds with the exclusion of the less active higher molecular weight basic aluminum compounds.
2. Prior Art
Basic aluminum compounds, particularly, basic aluminum halides, have long been used as antiperspirants. Generally, such basic aluminum compounds are, in the presence of water, complexes made up of mixtures of polymeric species of various sizes and molecular structures. It is known that basic polymeric aluminum species exist which have increased antiperspirant activity. These increased active basic polymeric aluminum compounds have an aluminum to anion molar ratio of from 0.5 to 2.5:1 and are determinable by several different standard tests, for example, the Size Exclusion Chromatographic Test. These aluminum compounds have been called Band III Aluminum Compounds.
U.S. Pat. No. 3,873,686 to S. M. Beekman discloses the general practice of preparing aluminum chlorhydroxide Al.sub.2 (OH).sub.5 Cl by the procedure of reacting 5 atomic weights of aluminum with 1 mole of aluminum chloride in an aqueous solution at 80.degree. to 90.degree. C. followed by filtration to remove trace insolubles and then spray dried.
U.S. Pat. No. 4,359,456 to Gosling et al, which is incorporated herein by reference, discloses a process for preparing an increased active antiperspirant polymeric aluminum hydroxy halide by a conventional step of prolonged heating of an aqueous solution containing a basic aluminum compound having substantially the same empirical formula as the polymeric aluminum compound prepared. Low concentration of starting material and elevated temperature aging have been stated as being critical in obtaining good yields of the enhanced active aluminum compound. However, the other species of basic aluminum halides having lesser antiperspirant activity are still present.
German application P 2900711.0 describes basic aluminum chloride, bromide, iodide and nitrate compounds having enhanced antiperspirant activity which is obtained by the conventional step of heating aqueous solutions of the components under conditions leading to formation of a greater proportion of the lower molecular weight polymeric species having a size about 100 Angstroms together with the higher molecular weight species.
U.K. Patent Application GB 2048229A discloses an aluminum chlorohydroxide which comprises at least 45% by weight of an aluminum group of aluminum chlorhydroxide complexes which is characterized by exhibiting anomalous permeation and reaction rates in the gel permeation chromatography and ferron tests. The aluminum chlorhydroxide is prepared by the elevated temperature aging of aluminum chlorhydroxide in an aqueous medium.
European Patent Application 6739 discloses a process for preparing a greater percentage of enhanced antiperspirant active species of polymeric basic aluminum halides which have been referred to as Band III aluminum compounds that is found in combination with the Band I and Band II species. The process involves a conventional heating step and aging at elevated temperatures.
It is recognized that in the preparation of the polymeric aluminum compounds, there are many factors which must be considered in order to obtain a higher ratio of the desired Band III aluminum compounds. The starting materials, their concentration, the temperatures utilized in the process and the time of aging are all critical in avoiding a polymeric shift to one of the lesser desirable basic aluminum compounds. Since lower concentrations of starting materials has been considered as being critical for obtaining a higher ratio of the desired enhanced active compounds, low yields are expected to result in their production, but still the other species of the polymeric aluminum compounds are expected to be present.
Conventional aluminum chlorohydrate for example, WICKENOL 323, which is marketed by Wickhen Products, Inc., primarily consists of complex polymeric species which generally used for purposes of the invention are depicted as having the empirical formula: Al.sub.2 (OH).sub.6-a X.sub.a, wherein a is about 1.0 to 4.
In the Size Exclusion Chromatography Test which is referred herein, there are three major bands detected in conventional aluminum chlorohydrate compounds. The Band I species is the largest of the group having antiperspirant activity. The species which possesses increased sweat resistance is known as the Band III aluminum compound. This species has a lower molecular weight and shows only a small size band.
It should be understood that the above formula is greatly simplified and is intended to include basic aluminum chlorides containing coordinated or bound molecules of water as well as basic aluminum chloride polymers, complexes and mixtures of the above.
Particularly suitable for the purposes of the present invention are basic aluminum chlorides having a basicity in the range of about two-thirds to five-sixths; that is compounds of the above general formula having a predominance of units of Al.sub.2 (OH).sub.4 Cl.sub.2 and/or Al.sub.2 (OH).sub.5 Cl, such that the aluminum to chlorine mol ratio ranges from about 1.0 to 2.0.
Teagarden et al in the article entitled "Aluminum Chlorohydrate I: Structure Studies", Journal paper 8254, Purdue University Agricultural Experimental Station, West Lafayette, IN 47907 reports that X-ray diffraction and IR and Al-NMR spectroscopy indicates that aluminum chlorohydrate is composed of a central aluminum in a tetrahedral configuration surrounded by 12 aluminum atoms in octahedral configuration. The proposed structure of aluminum chlorohydrate is Al.sub.13 O.sub.4 (OH).sub.24 (H.sub.2 O).sub.12 Cl.sub.7.
Teagarden et al in the article entitled "Aluminum Chlorohydrate II: Physiochemical Properties", Journal paper 8254, Purdue University Agricultural Experimental Station, West Lafayette, IN 47907, reports that based on the reaction rate with ferron, the distribution of aluminum species in aluminum chlorohydrate can be classified as 4% monomeric aluminum, 8% small polycation and 88% large polycation.
Because of the volume limitations in aerosols, merely increasing the amount of polymer aluminum chlorohydrate to increase the amount of the enhanced antiperspirant active species of the aluminum compound is not always feasible. Isolation or separation of the enhanced active species from the lesser active species for use to increase their amounts would increase costs. It is therefore highly desirable to provide a process for increasing the percentage of the enhanced active Band III species which is produced in a single step process. It is even more desirable to prepare only Band III aluminum compounds. It is further desirable to produce the enhanced active Band III species in a single process operation without isolation and/or elevated temperature aging starting with conventional aluminum chloride or aluminum metal.